We propose to continue the study of the biologic relevance of the heterophile transplantation antigen (HT-A) in human transplantation in the following ways. (1) Continued pre-transplant matching of donors and recipients by the indirect method of testing for serum immunity to HT-A, and observing the long term survival of grafts. (2) Study the morphologic differences between HT-A and HL-A rejection by light, fluorescent, and electron microscopy. (3) Continue efforts to obtain HT-A in pure form from human tissues for direct allogeneic reactions. (4) Studying the tissue distribution of heterophile antigens by immunoelectron microscopy.